In recent years, the development of the Internet has made it possible for people to access large quantities of information in real time and to handle large quantities of information. Information is transmitted by copper wire, optical fiber and wirelessly, but optical fiber is particularly superior for sending large volumes of information at high speeds. In the future, optical fiber is expected to be installed in each home.
However, because at the terminal end information is processed using electric signals, not optical signals, an optical module has to be used between an optical fiber and a terminal in order to connect the optical fiber to the terminal. An optical module is a device that converts optical signals received from the optical fiber to electric signals and supplies the electric signals to the terminal, and converts electric signals from the terminal to optical signals that are supplied to the optical fiber. In the prior art, various types of optical module have been proposed.
Optical output level is an important parameter indicating optical module performance. High-speed data communication systems require high output levels. For example, while a passive optical network (PON) that operates at a transmission speed of 100 MB/sec requires an output level of at least around −10 dBm after a transmission of 20 km, a 1 GB/sec PON system requires an output level of at least around −1 dBm after a transmission of 20 km. Optical output levels can be effectively increased by using light-emitting components that have a high luminous efficiency or by improving a coupling efficiency between the light-emitting component and the optical fiber, but it difficult to obtain a sufficiently high output level by doing just that. In order to transmit data at higher speeds, it is essential to increase the drive current to the light-emitting components.
However, increasing the drive current used to drive light-emitting components also increases the heat that is given off, thus raising the temperature of the light-emitting components themselves. As light-emitting components become high temperature, their emission efficiency usually decreases, so when the component temperature is increased by radiated heat, it becomes necessary to further increase the drive current. In accordance with this vicious cycle, the drive current should be further increased. The reliability of the resulting products is therefore degraded.
Improving the heat dissipation property of the optical transceiver is an effective way of resolving this problem. European Patent Application Laid Open No. 1,241,502 and U.S. Patent Application Laid Open Nos. 2003/0053768 and 2003/0141090, for example, describe optical transceivers with enhanced heat dissipation. In each of these disclosures, the heat dissipation of the optical transceiver is improved by providing the transceiver casing with an irregular pattern.
However, since generally the light-emitting components are not in direct contact with the transceiver casing but are instead spaced apart therefrom, it is difficult for the optical transceivers described in the prior art documents effectively dissipate the heat generated by the light-emitting components. To a certain extent, this problem can be resolved by affixing a heat sink to the main housing of the optical modules. However, doing this increases the number of parts, and another problem is that the adhesive used to attach the heat sink degrades the thermal conductivity to the heat sink, making it impossible to ensure an adequate heat dissipation property.